'The right kind of hollow' ... David Fincher at last month's Golden Globes. Photograph: Rex Features

For at least a year, David Fincher's name seemed all but engraved on the best director Oscar. The advance buzz on The Social Network, his Facebook drama released here in October, was unprecedented. The critics went wild, the public followed suit, and soon the Golden Globe for best director was his, along with eight Oscar nominations, including best picture. Then came the upset: last Saturday, the Director's Guild of America gave its top prize to Tom Hooper, for The King's Speech. Only six times in its 63-year history has its top prize not gone to someone who then went on to win the Oscar.

What happened? Did The Social Network lose momentum? Fincher is talking to me, after all, to promote the film's DVD release in the UK; it's rare for such a thing to happen before Oscar night. At the time of our talking, there had been barely a batsqueak of scepticism that it was anything other than a gong-gobbling masterpiece.

One detractor, though, was critic and novelist Zadie Smith, who wrote in the New York Review of Books that she had a problem with The Social Network being a film "about 2.0 people made by 1.0 people". Fincher, 48, and his screenwriter Aaron Sorkin, 49, had, she felt, ascribed inappropriately old-fashioned motives to Mark Zuckerberg, shown in the movie dreaming up the site after a bruising break-up, and then fighting lawsuits from the Winklevoss twins, who claim he ripped off their idea, and from his ex-best friend and financial wingman Eduardo Saverin.

Fincher, baby-faced over breakfast tea in London, isn't fazed. "Who's Zadie Smith?" he asks. "I think the film is probably a pretty good meatloaf of good old dramatic values held together with some 2.0 extender." While he doesn't feel out of kilter with the Facebook generation, he says he has no great affinity for things like building a website. "It's not very dramatic or photogenic, but I don't think it's a lesser form of creation. I have a healthy disdain for the hypocrisy of the notion of this interconnected world. But I don't think that makes me some old fuck with an axe to grind." He smiles. "I acknowledge that video games could be an amazing art form – but not until the people making them go back a bit, to the Aaron Sorkin way of thinking about character and motivation."

When Fincher first watched the finished film, however, it was Sorkin's work that prompted some misgivings. "My first thought was, 'It's a bit slight.' But there's kind of a riptide to Sorkin's glibness. A lot of what he says is the sparkle on the surface, but there's a poignant discomfort underneath. He's such a verbal savage, but at first I did think, 'It's too fast and there's something slight about it.' Then I walked away, and an hour later I thought, 'No, it's OK, it really resonates, it leaves you with the right kind of hollow.' It's like sushi: you might be hungry again in a bit, but you ate something pretty spectacular."

This "right kind of hollow" comes, he thinks, from never quite nailing what makes the central character tick. Though Fincher recoils at the thought of lumping Zuckerberg in with the loner sociopaths that populate much of his previous work – Seven, Fight Club, Panic Room, Zodiac – he steered Jesse Eisenberg, playing the lead, towards maximum opacity by making references to Robert De Niro's character in Taxi Driver. "I kept saying, 'I don't know where Travis Bickle is from or what made him do what he did. I don't know and I don't care. That's what makes him compelling.' I don't think you can explain how somebody hits the bullseye like this. It's like picking gnatshit out of pepper."

Fincher, similarly, is a man who becomes only marginally less mysterious after time in his company. He comes across as a courteous, efficient pragmatist, a director whose experience of everything from ads (he met his partner, Ceán Chaffin, while doing one for Coca-Cola) to music videos (including Madonna's Vogue) to films has given him remarkable financial realism. And Fincher Inc is certainly a heavyweight concern now: 2008's The Curious Case of Benjamin Button cost $150m and took $334m; the stakes for his forthcoming project, filming Stieg Larsson's novels with Daniel Craig, are even greater (his take on Girl With the Dragon Tattoo is due this Christmas).

Talking about technology, he scorns the idea that mobile phones have given us greater control. "I could call my office and find out what is going on. But that would assume that: a) people in the office know what the fuck's going on; b) that you get a hold of them; c) that they will call you back in a timely manner; and d) that you can get reception." It's an infectious attitude: the director as MD, full-throttle, no fools. At one point, the door opens and Daniel Craig walks in, then sits down to wait for rehearsals to begin, so undiva-like he could be in a doctor's waiting room.

Fincher is clear-headed about his responsibilities – to real-life subjects, collaborators, investors and audiences. But it's his attitude to audiences that shows that his lack of pretension has nothing to do with a lack of artistic ambition. "My responsibility is to unsettle people. There are hundreds of movies a year lobbying to be man's best friend. And I don't feel I need to add to that. I like popcorn movies but, as part of a healthy balance, one of the other food groups could be semi-challenging adult-ish fare."

Loners who stop the world

That's what he dishes up: exhilarating, frightening, mature thrillers soaked in paranoia, on time, to budget, and no less nutritious for it. After the gloopy wobble of Benjamin Button, The Social Network marks both a return to form and to his nagging preoccupation: that the world can be turned on its axis by the actions of one powerful – possibly dangerous – person. In the flesh, Fincher admits he thinks most people bend the truth for their own ends whenever they open their mouths. Or as he puts it: "Most interpersonal communication is hair-splitting recontextualisation, trying to shift someone else off their position."

It comes as no surprise to find him vociferous in his defence of Sean Parker, the slick former boss of Napster, the file-sharing website that all but destroyed music sales before going legit. In The Social Network, Parker takes Zuckerberg under his wing and apparently unseats Saverin from the nest. "I find Sean to be utterly entertaining and magnetic and responsible. It's like the older brother saying, 'Don't fall in love with this girl – she's bad news.' I didn't see anything Machiavellian about it. It seemed to me he was making real sense. He didn't want to see [Zuckerburg] make mistakes, wanted someone good watching his back."

While Fincher can see reasons to root for all his film's protagonists ("I don't think anybody in it's an asshole"), not everyone feels the same way – and this hesitancy could hobble his Oscar chances. True Grit and The King's Speech, also up for best picture, have a reassuring conservatism, but The Social Network's take on the American dream is more unsettling. It's this aspect that tickles Fincher, a high school graduate who eschewed film school: his own journey to the very top isn't a million miles from Zuckerberg's.

"At Harvard," he says, "you have buildings designated for this and that, yet probably the biggest thing that's ever been associated with Harvard was invented by one guy who sequestered himself away in a dorm corner. You've got this wealth and this colonial castle, but in the end all he needed was $69 per month for the server, $39 for electricity, and $159 for the Red Bull.

"Harvard is this breeding ground for this 19th-century notion of entrepreneurship, designed to turn out these capitalists who could train a workforce, build a factory and turn out a product that somebody purchased, cranked and drove off into the sunset. And now we're in a world where we don't need all those people."

He downs his coffee, poured unceremoniously on to the dregs of his tea. "I thought that was kind of cool. More irony for the meatloaf."